phy: usb: sunplus: Fix potential null-ptr-deref in sp_usb_phy_probe()

sp_usb_phy_probe() will call platform_get_resource_byname() that may fail
and return NULL. devm_ioremap() will use usbphy->moon4_res_mem->start as
input, which may causes null-ptr-deref. Check the ret value of
platform_get_resource_byname() to avoid the null-ptr-deref.

Fixes: 99d9ccd9

 ("phy: usb: Add USB2.0 phy driver for Sunplus SP7021")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Link: https://lore.kernel.org/r/20221125021222.25687-1-shangxiaojing@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>